/*
 * Copyright (C) 2023 杭州白书科技有限公司
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package xyz.playedu.api.util;

/** Base64工具类 */
public final class Base64Util {
    private static final int BASE_LENGTH = 128;
    private static final int LOOK_UP_LENGTH = 64;
    private static final int TWENTY_FOUR_BIT_GROUP = 24;
    private static final int EIGHT_BIT = 8;
    private static final int SIXTEEN_BIT = 16;
    private static final int FOUR_BYTE = 4;
    private static final int SIGN = -128;
    private static final char PAD = '=';
    private static final byte[] base64Alphabet = new byte[BASE_LENGTH];
    private static final char[] lookUpBase64Alphabet = new char[LOOK_UP_LENGTH];

    static {
        for (int i = 0; i < BASE_LENGTH; ++i) {
            base64Alphabet[i] = -1;
        }

        for (int i = 'Z'; i >= 'A'; i--) {
            base64Alphabet[i] = (byte) (i - 'A');
        }

        for (int i = 'z'; i >= 'a'; i--) {
            base64Alphabet[i] = (byte) (i - 'a' + 26);
        }

        for (int i = '9'; i >= '0'; i--) {
            base64Alphabet[i] = (byte) (i - '0' + 52);
        }

        base64Alphabet['+'] = 62;
        base64Alphabet['/'] = 63;

        for (int i = 0; i <= 25; i++) {
            lookUpBase64Alphabet[i] = (char) ('A' + i);
        }

        for (int i = 26, j = 0; i <= 51; i++, j++) {
            lookUpBase64Alphabet[i] = (char) ('a' + j);
        }

        for (int i = 52, j = 0; i <= 61; i++, j++) {
            lookUpBase64Alphabet[i] = (char) ('0' + j);
        }

        lookUpBase64Alphabet[62] = '+';
        lookUpBase64Alphabet[63] = '/';
    }

    /**
     * 转码
     *
     * @param binaryData 未转码数据
     * @return 转码后数据串
     */
    public static String encode(byte[] binaryData) {
        if (binaryData == null) {
            return null;
        }

        int lengthDataBits = binaryData.length * EIGHT_BIT;
        if (lengthDataBits == 0) {
            return "";
        }

        int fewerThan24bits = lengthDataBits % TWENTY_FOUR_BIT_GROUP;
        int numberTriplets = lengthDataBits / TWENTY_FOUR_BIT_GROUP;
        int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1 : numberTriplets;
        char[] encodedData;

        encodedData = new char[numberQuartet * 4];

        byte k, l, b1, b2, b3;
        int encodedIndex = 0;
        int dataIndex = 0;

        for (int i = 0; i < numberTriplets; i++) {
            b1 = binaryData[dataIndex++];
            b2 = binaryData[dataIndex++];
            b3 = binaryData[dataIndex++];

            k = (byte) (b1 & 0x03);
            l = (byte) (b2 & 0x0f);

            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);
            byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);
            byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6) : (byte) ((b3) >> 6 ^ 0xfc);

            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2) | val3];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f];
        }

        if (fewerThan24bits == EIGHT_BIT) {
            b1 = binaryData[dataIndex];
            k = (byte) (b1 & 0x03);
            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4];
            encodedData[encodedIndex++] = PAD;
            encodedData[encodedIndex++] = PAD;
        } else if (fewerThan24bits == SIXTEEN_BIT) {
            b1 = binaryData[dataIndex];
            b2 = binaryData[dataIndex + 1];
            l = (byte) (b2 & 0x0f);
            k = (byte) (b1 & 0x03);
            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);
            byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);

            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2];
            encodedData[encodedIndex++] = PAD;
        }
        return new String(encodedData);
    }

    /**
     * 解码
     *
     * @param encoded 已转码数据
     * @return 解码后数据
     */
    public static byte[] decode(String encoded) {
        if (encoded == null) {
            return null;
        }

        char[] base64Data = encoded.toCharArray();
        int len = removeWhiteSpace(base64Data);

        if (len % FOUR_BYTE != 0) {
            return null;
        }

        int numberQuadruple = (len / FOUR_BYTE);
        if (numberQuadruple == 0) {
            return new byte[0];
        }

        byte[] decodedData;
        byte b1, b2, b3, b4;
        char d1, d2, d3, d4;

        int i = 0;
        int encodedIndex = 0;
        int dataIndex = 0;
        decodedData = new byte[(numberQuadruple) * 3];

        for (; i < numberQuadruple - 1; i++) {

            if (!isData((d1 = base64Data[dataIndex++]))
                    || !isData((d2 = base64Data[dataIndex++]))
                    || !isData((d3 = base64Data[dataIndex++]))
                    || !isData((d4 = base64Data[dataIndex++]))) {
                return null;
            }

            b1 = base64Alphabet[d1];
            b2 = base64Alphabet[d2];
            b3 = base64Alphabet[d3];
            b4 = base64Alphabet[d4];

            decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
            decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
            decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);
        }

        if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++]))) {
            return null;
        }

        b1 = base64Alphabet[d1];
        b2 = base64Alphabet[d2];
        d3 = base64Data[dataIndex++];
        d4 = base64Data[dataIndex++];
        if (!isData((d3)) || !isData((d4))) {
            if (isPad(d3) && isPad(d4)) {
                if ((b2 & 0xf) != 0) {
                    return null;
                }
                byte[] tmp = new byte[i * 3 + 1];
                System.arraycopy(decodedData, 0, tmp, 0, i * 3);
                tmp[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
                return tmp;
            } else if (!isPad(d3) && isPad(d4)) {
                b3 = base64Alphabet[d3];
                if ((b3 & 0x3) != 0) {
                    return null;
                }
                byte[] tmp = new byte[i * 3 + 2];
                System.arraycopy(decodedData, 0, tmp, 0, i * 3);
                tmp[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
                tmp[encodedIndex] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
                return tmp;
            } else {
                return null;
            }
        } else {
            b3 = base64Alphabet[d3];
            b4 = base64Alphabet[d4];
            decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
            decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
            decodedData[encodedIndex++] = (byte) (b4 | b3 << 6);
        }
        return decodedData;
    }

    /**
     * 是否空白
     *
     * @param octEct 位
     * @return boolean
     */
    private static boolean isWhiteSpace(char octEct) {
        return (octEct == 0x20 || octEct == 0xd || octEct == 0xa || octEct == 0x9);
    }

    /**
     * 是否填充
     *
     * @param octEct 位
     * @return boolean
     */
    private static boolean isPad(char octEct) {
        return (octEct == PAD);
    }

    /**
     * 是否数据
     *
     * @param octEct 位
     * @return Boolean
     */
    private static Boolean isData(char octEct) {
        return (octEct < BASE_LENGTH && base64Alphabet[octEct] != -1);
    }

    /**
     * 移除空白
     *
     * @param data 数据
     * @return int
     */
    private static int removeWhiteSpace(char[] data) {
        if (data == null) {
            return 0;
        }

        int newSize = 0;
        int len = data.length;
        for (int i = 0; i < len; i++) {
            if (!isWhiteSpace(data[i])) {
                data[newSize++] = data[i];
            }
        }
        return newSize;
    }
}
